The present invention relates to a method and an arrangement for determining angular velocities with the aid of an optical fiber ring interferometer, wherein light waves which pass through at least one optical fiber winding of the interferometer are sinusoidally phase modulated and the amplitudes of several spectral lines of the interfering light waves exiting from the optical fiber are determined, with the Sagnac phase, which is proportional to the angular velocity, being determined therefrom.
A method and an arrangement of this type is disclosed in U.S. Pat. No. 4,549,806 which issued on Oct. 29, 1985, the subject matter of which being incorporated herein by reference. This known ring interferometer includes an optical fiber which forms an annular path for the light in which two oppositely directed light waves are propagated. Upon leaving the optical fiber, these light waves interfere with one another. This interference depends on the angular velocity with which the optical fiber forming the at least one winding is rotated. Thus, the angular velocity is proportional to the phase difference between the two light waves that have passed through the optical fiber in opposite directions. This phase difference, the so-called Sagnac phase shift, can be determined from the amplitudes of two spectral lines of the interference light leaving the optical fiber as described in U.S. Pat. No. 4,549,806. However, this method for determining the Sagnac phase shift requires that the modulation index of the phase modulation taking place at the output of the light path be kept at a constant value by means of a control circuit in order to accurately and reliably measure the phase shift.